The invention is directed to power operated tools that are adjustable to provide either a positive drive connection between the motor and tool element or a drive connection that can be established and interrupted at will by the person operating the tool when required by the nature of the work.
Although not necessarily limited thereto, the invention is advantageously embodied in a portable electric tool that combines the features of a drill and a screwdriver in an efficient and compact unit that is especially easy to operate.
Power tools such as a combination drill and screwdriver have clutch members which include a first clutch rotatably mounted in the housing of the tool. An annular bearing is movably mounted in a bore of the housing. A second clutch is rotatably mounted in the annular bearing and is movable relative to the first clutch between the first position whereat the two clutches firmly engage; and, a second position whereat the second clutch is positioned axially away from the first clutch so that the clutches are disengaged. The two clutches are held apart with the aid of biasing means usually in the form of a coil spring which biases the second clutch away from the first clutch. This condition corresponds to the screwdriver mode. When the operator has the tool in the screwdriving mode, he places the tool against the fastener and then exerts pressure on the tool causing the clutches to engage and the screwdriver bit to turn. When the fastener tightens in the workpiece, a ratcheting action occurs because the clutches become disengaged thereby preventing the fastener from becoming stripped or damaged.
In the prior art devices of which we are aware, the adjustment of the clutches so as to bring them into the drill mode is achieved as suggested for example by U.S. Pat. No. 2,950,626 to Short wherein an annular bearing holds a spindle with the second clutch integral therewith. The bearing threadably engages the housing of the tool so that when the operator rotates the annular bearing, it causes the second clutch to be moved axially so as to come into firm, positive engagement with the first clutch driven by the tool motor thereby placing the tool in the drill mode.
The device of Short includes a spindle bearing threadably engaging a housing and has the disadvantage that the operator must rotate the spindle bearing as much as a whole revolution in order to cause the clutches to positively engage for the drill mode. Further, there is the disadvantage that housing must be specially threaded to accommodate the spindle bearing which is a costly manufacturing step.
Also, the means for holding the spindle bearing in place and the second clutch in position during operation of the tool in the drill mode has the disadvantage that during continuous operation, the clutches can become disengaged. For example, the above-mentioned patent to Short discloses a Nylon plug mounted in the motor housing of the tool which can be adjusted so as to press hard against the outer thread of the spindle bearing with which the spindle bearing threadably engages the motor housing. However, in time, the plug wears and it becomes necessary to frequently retighten the plug in the housing against this thread.